Squamous cell carcinoma (SCC) is a type of nonmelanoma skin cancer derived from the epidermis and is one of the most frequent human malignancies. SCCs characteristically exhibit a high propensity for invasion and metastasis and may be lethal. The molecular events underlying the pathogenesis of SCC have been actively studied;however, no resulting preventative or therapeutic strategies, apart from surgery, have successfully targeted this lesion. CD200, also referred as OX-2, is a widely expressed type I transmembrane glycoprotein that is thought to primarily mediate the suppression of myeloid cell function through its receptor, CD200R, in various tissues including the skin. CD200 induction has been reported in tumorigenic keratinocytes;however, the impact of CD200 in otherwise normal epithelium on the initiation and course of SCC pathogenesis is unknown. Our preliminary findings show that induction of CD200 is a hallmark of both murine and human cutaneous SCC metastasis to the lymph node and that CD200-positive metastatic keratinocytes appear to directly interact with CD200R-positive myeloid (CD11b+) cells indicating that the migration of SCC cells may be dependent on their ability to directly suppress the anti-tumor responses of CD200R-positive immune cells. Overall, the studies outlined in this proposal are aimed at defining the role of CD200 in cutaneous SCC formation and metastasis. We will test the hypothesis that CD200 regulates the metastatic capacity of cutaneous SCC by directly suppressing the anti-tumor function of CD200R-positive myeloid cells. To test this hypothesis, we will identify all subtypes of CD200 and CD200R-positive cells in cutaneous SCC and SCC-derived lymph node metastases in order to fully characterize the putative CD200-CD200R cell interactions that may contribute to metastatic SCC immune privilege. We will assess the capacity of CD200 to stimulate SCC formation and metastasis in a transgenic mouse model that targets CD200 to the proliferative layer of the epidermis under the control of doxycycline. Finally, we will ablate CD200 in metastatic SCC cells and assess its impact on myeloid cell activity and the ability of CD200-deficient SCC cells to reconstitute lymph node metastases in vivo. The ability to pinpoint these critical interactions between immune and metastatic SCC cells will provide better insight into the mechanisms of cancer immunity and lead to more effective therapeutic strategies for these potentially fatal cancers. PUBLIC HEALTH RELEVANCE: The process of metastasis has been well documented for a wide variety of cancers;however, despite current progress metastatic cancers still account for almost all of the deaths related to solid tumors. This proposal aims to identify certain molecules that bestow immune privilege on cancer cells and stimulate the metastatic process with the hope of introducing new targets to advance clinical treatment of this lethal disease.